Your pressure was probably low. 2.3 bar is 33 psi. That's low for track use. I would start out with 37-38 psi and try to keep it around 40 psi (measure hot pressure in between sessions and let air out if it is too high). It is true that the stock suspension does not have a whole lot of negative camber up front, but you'd have to be driving pretty hard and the car would need to be pushing hard into corners (understeer) for this to happen so quickly due to a camber issue. I don't get the impression you were driving that hard. At any rate, this is not a big deal. You just scruffed the tires on the outside a little. Just use higher pressure next time. But if you will track frequently, a dedicated set of wheels/tires would save you money in the long run indeed.